<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
    </style>
    <style>
        .red{
            color: red;
        }
    </style>
    <p class="red">
        hello world
    </p>
    <p class="red">
        hello Java
    </p>
    <style>
        #cpp {
            color: red;
        }
        
        /*选择器1 选择器2*/
        /*注意中间必须有空格*/
        ul .name{/*中ul标签里面是class为name的元素*/
            color: #000;
        }

        ul.name{/*找ul同时class为name的元素*/
            color: aqua;
        }

        ul>.name{
            color: aqua;
        }

        ul>.name, ul>li{
            color: aqua;
        }

        .zero {
            color: rgb(255, 0, 0);
            color: rgba(red, green, blue, alpha);
        }
        .one {
            color: #00ff00;
            text-align: center;
            text-align: left;
            text-align: right;
        }
    </style>
    <p id = "cpp">
        hello C++
    </p> -->

    <!-- <table width="400px" border="1px" cellspacing=0>
        <tr class="one">
            <td>1</td>
            <td>2</td>
            <td>3</td>
        </tr>
        <tr class="two">
            <td>4</td>
            <td>5</td>
            <td>6</td>
        </tr>
        <tr class="three">
            <td>7</td>
            <td>8</td>
            <td>9</td>
        </tr>
    </table>
    <style>
        table td {
            text-align: center;
            font-size: 16px;
        }
        .one {
            color: red;
            text-decoration: underline;
        }
        .two {
            color: green;
            text-decoration: line-through;
        }
        .three {
            color: blue;
            font-weight: bolder;
            
        }
    </style> -->
    <!-- <p>
        iore
    </p>
    <style>
        p {
            text-indent: 2em;
            background-color: black;/* 用法类似color */
            background-image: url(rose.jpg);
            /* 平铺 */
            background-repeat: repeat;
            /* 不平铺 */
            background-repeat: no-repeat;
            /* 水平平铺 */
            background-repeat: repeat-x;
            /* 垂直平铺 */
            background-repeat: repeat-y
            /* 修改图片位置 */
            /* background-position x y; */
        }
        .one {
            border-radius: 50%;
            display: block;
            box-sizing: border-box;
            border: 2px;
            padding: 2px;
            padding-left: 0%;
            padding-right: 10%;
            padding-top: 0%;
            padding-bottom: 0%;
            /* 文本的水平居中 */
            text-align: center;
            /* 文本的垂直居中 */
            line-height : height ;
            /* 元素的水平居中 */
            margin: 0 auto;
            display: flex;

            /* 靠左排列 */
            justify-content: start;
            /* 靠右排列 */
            justify-content: end;
            /* 居中排列 */
            justify-content: center;
            /* 元素等分间隔 */
            justify-content: space-between;
            /* 元素等分间隔，包括最左边和最右边 */
            justify-content: space-around;

            align-items: 0;
        }
    </style> -->
    <!-- <div class="parent"></div>
    <style>
        .parent {
            width: 500px;
            height: 300px;
            border: 5px;

            border-top: blue solid;
            border-bottom: yellow solid;
            border-left: red solid;
            border-right: green solid;

            background-image: url(../homeworkcss/背景.png);
            background-size: 100px 100px;
            background-position: center;
            background-repeat: no-repeat;
        }
    </style> -->
    <!-- <div class="parent">
        <div class="nav">我是导航栏</div>
        <div class="body">
            <div class="left">我是左边栏</div>
            <div class="content">我是内容区</div>
            <div class="right">我是右边栏</div>
        </div>
    </div>
    <style>
        * {
            margin: 0px;
            padding: 0px;
            box-sizing: border-box;
        }

        .parent {
            background-color: gray;
            color: white;
            font-size: 20px;
        }

        .nav {
            background-color: red;
            height: 50px;
            text-align: center;
            line-height: 50px;
        }
        
        .body {
            display: flex;
            
            color: white;
            height: 500px;
            line-height: 500px;
            text-align: center;
        }

        .left, .right {
            background-color: green;
            width: 20%;
        }

        .content {
            width: 80%;
        }
        
    </style> -->
    <div class="parent">
        <div class="red"></div>
        <div class="green"></div>
        <div class="yellow"></div>
    </div>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        .parent {
            background-color: gray;
            padding: 25px;
            margin: 0 auto;
            width: 200px;
            height: 600px;
        }

        .red, .green, .yellow {
            width: 150px;
            height: 150px;
            border-radius: 50%;
        }

        .red {
            background-color: red;
        }

        .green {
            background-color: green;
            margin-top: 50px;
        }

        .yellow {
            background-color: orange;
            margin-top: 50px;
        }
    </style>
</body>
</html>